1. Field of the Invention
The present invention relates to an actuator which makes it possible to move a slider linearly reciprocatively along a frame in accordance with a driving action of a driving source.
2. Description of the Related Art
A transport means such as an actuator has been hitherto used, for example, in order to transport a workpiece.
A conventional actuator is shown in FIG. 14 (see, for example, Japanese Laid-Open Patent Publication Nos. 8-126247 and 8-130849).
The conventional actuator comprises a base 1 which is integrally formed with a bottom wall and a pair of side walls perpendicular to the bottom wall, a ball screw shaft 2 which is rotatable in accordance with a driving action of an unillustrated servo motor, and a slider 4 which is displaceable in the axial direction of the base 1 by the aid of a ball nut 3 screw-engaged with the ball screw shaft 2.
Base-side grooves 5, each of which has a rectangular cross section, are formed on inner wall surfaces of the side walls respectively. Slider-side grooves 6, each of which has the same shape as that of the base-side groove 5, are formed at portions of the slider 4 opposed to the base-side grooves 5. Base-side rails 7, each of which has a rectangular cross section corresponding to the base-side groove 5 and each of which has a ball-rolling groove formed on a side surface thereof, are installed to the base-side grooves 5. On the other hand, slider-side rails 8, each of which has a rectangular cross section corresponding to the slider-side groove 6 and each of which has a ball-rolling groove formed on a side surface thereof, are installed to the slider-side grooves 6.
A plurality of balls 9, which circulate and roll in accordance with the displacement of the slider 4, are installed between the mutually opposing ball-rolling grooves of the base-side rails 7 and the ball-rolling grooves of the slider-side rails 8.
However, in the conventional actuator, each of the base-side rail 7 installed to the base-side groove 5 and the slider-side rail 8 installed to the slider-side groove 6 is formed to have the rectangular cross section. Therefore, when the balls 9 roll along the ball-rolling grooves as endless circulating tracks, the stress is concentrated on rectangular angular portions of the base-side groove 5 and the slider-side groove 6 (see FIG. 15). Therefore, the durability of the base-side rail 7 and the slider-side rail 8 low.
Further, it is desirable to reduce the size of a shape of a flange section of the ball nut 3 to which the ball screw shaft 2 is screw-engaged, and decrease the installation area with respect to the slider 4 so that the arrangement of the ball-rolling hole as the endless circulating track in the slider 4 can be designed more freely.
An object of the present invention is to provide an actuator which allows the arrangement of a ball-rolling hole in a slider to be performed more freely and mitigates the concentration of stress exerted by the external force.
According to the present invention, a first guide rail, which is installed to a first long groove, is formed to have a circular arc-shaped cross section, and a second guide rail, which is installed to a second long groove, is formed to have a circular arc-shaped cross section. Accordingly, it is possible to mitigate the concentration of stress by the external force, and it is possible to improve the durability of the first guide rail and the second guide rail.
Further, according to the present invention, a first slide cover and a second slide cover have different shapes. A surface area of the first slide cover is smaller than a surface area of the second slide cover. Accordingly, the arrangement of a ball-rolling hole in a slider can be designed more freely.
Further, according to the present invention, the first slide cover having a small surface area is installed to a first end side in the axial direction of a slider. The second slide cover having a large surface area is installed to a second end side of the slider arranged with a driving source disposed on the side opposite to the first slide cover. Accordingly, it is possible to ensure the orientation of assembling.